The present invention relates generally to the field of biochemical laboratory instrumentation for different applications of measuring properties of samples on e.g. microtitration plates and corresponding sample supports. More particularly the invention relates to the improved, reliable and more accurate instrumental features of equipment used as e.g. fluorometers, photometers and luminometers.
The routine work and also the research work in analytical biochemical laboratories and in clinical laboratories are often based on different tags or labels coupled on macromolecules under inspection. The typical labels used are different radioactive isotopes, enzymes, different fluorescent molecules and e.g. fluorescent chelates of rare earth metals.
The detection of enzyme labels can be performed by utilizing its natural biochemical function, i.e. to alter the physical properties of molecules. In enzyme immunoassays colourless substances are catalysed by enzyme to colourful substances or non-fluorescent substances to fluorescent substances.
The colourful substances are measured with absorption, i.e. photometric measurement. In the photometric measurement the intensity of filtered and stabilized beam is first measured without any sample and then the sample inside one plate is measured. The absorbance i.e. the absorption values are then calculated.
The fluorescent measurement is generally used for measuring quantities of fluorescent label substance in a sample. The most photoluminescence labels are based on molecular photoluminescence process. In this process optical radiation is absorbed by the ground state of a molecule. Due to the absorption of energy the quantum molecule rises into higher excited state. After the fast vibrational relaxation the molecule returns back to its ground state and the excess energy is released as an optical quantum. Due to losses in this process the average absorbed energies are higher than the average emitted energies.
A further measurement method is chemiluminescence measurement where emission of a substance is measured from a sample without excitation by illumination. Thus any photoluminometer can also be used as a chemiluminometer.
The typical instruments in analytical chemical research laboratories are the different spectroscopic instruments. Many of them are utilizing optical region of electromagnetic spectrum. The two common types of instruments are the spectrophotometers and the spectrofluorometers. These instruments comprise usually one or two wavelength dispersion devices, like monochromators. The dispersion devices make them capable to perform photometric and luminescence measurements throughout the optical spectrum.
FIG. 1 illustrates an advanced prior art optical analyser, especially the optical components and the different optical paths. The instrument has two illumination sources, a continuous wave lamp (cw-lamp) 112a and a pulse lamp 112b. The cw-lamp can be used for continuous wave photoluminescence excitation and for absorption measurements.
Infrared part of radiation from the cw-lamp 112a is absorbed by a filter 104, and after transiting a stray-light aperture plate 105, the optical radiation is collimated with a lens 115a through an interference filter 114a located in a filter wheel 114.
The light beam is focused with a lens 113a, similar to the lens 114a, into a light guide 118, which isolates the measuring head thermally and mechanically. It also shields the measuring unit for the stray light from the cw-lamp. The optical radiation from an output aperture plate 106 of a light guide 118 is collimated with a lens 107, similar to the lens 115a. The radiation beam is reflected by a beam-splitter mirror 141 inside a mirror block 140, and passed through a sample well 181 and through an entrance window 122 of a photometric detector unit 132.
The mirror block 140 is located on the upper side of the sample. Its function is to reflect the horizontal light beam from the selected lamp downwards to the sample and to reflect a portion of this beam by a mirror 143 into a reference photodiode 119, and also to allow the emission from the sample to travel upwards to the detector 132.
The emission unit comprises optical components, which are lenses 133, 135, a filter 134a in filter slide 134, a combined shutter and aperture slide 136 and a detector 132, such as a photo-multiplier. The detector 132 is used in the fast photon counting mode where the pulses from photo-multiplier anode are first amplified and then fed through a fast comparator 191 and gate 192 counter 193. The comparator rejects the pulses, which are lower than the pre-adjusted reference level. The fast counting electronics is equipped with a gate in the front of the counter. This gate is used in overall timings of the measurements.
The pulse-lamp unit is used in time-resolved photoluminescence measurement for long-living luminescence emission. It comprises a second lamp 112b, lenses 115b, 113b, and optical filters 114b in a filter slide for wavelength isolation. When this second lamp is used the mirror 141 must be rotated by 90 degrees in order to reflect the radiation to the sample. This can be achieved by using different optical modules for the two lamps.
There are certain limitations related to the prior art technology. When different optical modules are used for different measurements the optical module is usually changed when the measurement mode is changed. As the optical modules are manually handled the lenses of the optical module easily become unclean. This causes attenuation of the optical beams and thus may make the measurement results less accurate and less reliable. Another limitation of the prior art solutions relates to comparability of different measurements. When different optical modules are used for different measurements the optical path may be different and cause that the location or size of the measurement area in the sample may be vary for different types of measurements.